Although thin film semiconductor devices, i.e. semiconductor devices in which the active portion of the device is a thin film of semiconductor material, have been known for some time, there has recently developed a need for making integrated circuits which include thin film semiconductor devices on an insulating substrate. For example, for display devices, such as liquid crystal displays, it has been found desirable to be able to form the drive circuit for the display device directly on one of the glass plates which form the liquid crystal display device. One type of semiconductor device which is desirable for such an integrated circuit is a back-to-back diode, i.e. two diodes in series but with the polarity of one being reversed to that of the other.